The invention relates to a control system for an internal combustion engine with externally supplied ignition, having an intake tube, a throttle valve mounted in the intake tube, a controllable bypass around the throttle valve and a fuel metering system.
A controllable throttle valve bypass serves as a rule to provide a capability of establishing a predetermined rpm during idling or in other words when the throttle valve is closed. If in such known systems the air quantity is measured in order to determined the required fuel quantity, then the air flow rate meter is disposed ahead of the bypass branching point upstream of the throttle valve, so that the air component in the bypass is detected as well. In this manner, so-called charge-level regulators are attained, which have constant fuel/air ratios.
A disadvantage of these known systems is that they can only be applied to a limited extent in systems which measure the air flow rate; thus it is not possible, for instance, to use fuel metering systems which determine the fuel quantity solely in accordance with the rpm and the position of the throttle valve. Furthermore, in the known systems the fuel-air mixture cannot be influenced or in other words optimized during idling, because a fuel quantity value is determined for every total air quantity. Also, the bypass of the known type cannot be used together with an optimal engine regulating means in terms of fuel consumption. This is because for the sake of optimizing fuel consumption, the air quantity oscillates while the fuel quantity remains constant.